Sorting MAP

[Waez Ali]

Hi All,

I am reading some data from properties file, & want sort this based on keys and in some cases based on values.

E.g test.properties

1 = Hi
2 = hello
3 = Bye
4 = Thank You
5 = Thank You
6 = Bye



When I load the above data into my properties object data is n more sorted.

Can someone please help me out to sort this data after reading it from properties file ?

Thanks in advance.
Waez Ali.

[David O'Meara]

Sounds like you want a java.util.TreeMap
Check the API

[Dariusz Kordonski]

TreeMap will sort the properties according to natural ordering of keys (unless you explicitly specify your own Comparator). If you want to have your properties in the order, in which they exist in file, I guess you would have to use Scanner class.

[Dariusz Kordonski]

I saw on the other post that you would like to sort properties by values without losing duplicate values. I don't know of any built-in API that could be used to accomplish this directly. You may use a kind of helper class, check out the example code:

public class SortMapByValue {
 
    public static void main(String[] args) {
        
       Properties props = new Properties();// this is fake - init props properly
       List<Entry> lst = new ArrayList<Entry>();
       //convert props to list of entries
       for(String name : props.stringPropertyNames()) {
           lst.add(new Entry(name, props.getProperty(name)));           
       }
       //sort - entry implements comparable
       Collections.sort(lst);
       //convert to ordered map
       Map<String, String> map = new LinkedHashMap<String,String>();
       for(Entry entry : lst) {
           map.put(entry.name, entry.value);
       }    
    }
 
    static class Entry implements Comparable<Entry> {
 
        String name;
        String value;
 
        public Entry(String nm, String val) {
            name = nm;
            value = val;
        }
        public int compareTo(Entry o) {
            return value.compareTo(o.value);
        }
    }
}    

But maybe there is an easier solution...

[Jesper de Jong]

TreeMap keeps the entries of the map in the natural order of the keys (or in the order specified by a custom comparator) as already mentioned above.

If you want to keep the entries in the map in the order that they were added to the map, use LinkedHashMap (look it up in the API documentation for more info).